1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a Cu wire made of a metallic material mainly composed of Cu (copper).
2. Description of Related Art
In a highly integrated semiconductor device, Cu having higher conductivity than Al (aluminum) may be employed as the material for a wire. A wire made of Cu is embedded in a fine groove formed in an insulating film (an interlayer dielectric film) on a semiconductor substrate by a damascene process, since it is difficult to finely pattern Cu by dry etching.
In general, SiO2 is employed as the material for the insulating film. However, Cu has high diffusibility into SiO2. When the inner surface of the groove formed in the insulating film made of SiO2 and the wire made of Cu are directly in contact with each other, Cu diffuses into the insulating film. This diffusion tends to reduce the dielectric voltage of the insulating film. Therefore, a barrier film for preventing Cu from diffusing into the insulating film must be provided between the insulating film and the wire made of Cu.
A self-formation process employing a CuMn alloy is known as a technique of forming the barrier film. In the self-formation process, an alloy film made of an alloy of Cu and Mn (manganese) is formed on the surface of the insulating film including the inner surface of the groove by sputtering, in advance of formation of the wire. Then, a plating layer made of Cu is formed on the alloy film by plating. Thereafter heat treatment is performed, whereby Mn in the alloy film is bonded to Si (silicon) and O (oxygen) in the insulating film, and a barrier film made of MnxSiyOz (x, y and z: numbers greater than zero. MnxSiyOz is hereinafter simply referred to as “MnSiO”) is formed between the plating layer and the insulating film, i.e., on the inner surface of the groove.
Excess Mn not contributing to the formation of the barrier film diffuses into the plating layer made of Cu. If the quantity of Mn diffusing into the plating layer is large, Mn remains in the Cu wire formed by planarizing the plating layer, to increase the resistance of the wire. Therefore, the alloy film made of the CuMn alloy is preferably formed with a thickness necessary and sufficient for forming the barrier film.
When the alloy film is formed by sputtering, however, the CuMn alloy is harder to bond to the side surfaces of the groove as compared with the bottom surface thereof. If the alloy film is formed with a small thickness as a whole to have the thickness necessary and sufficient for forming the barrier film on the bottom surface of the groove, therefore, portions of the alloy film formed on the side surfaces of the groove are excessively reduced in thickness. Consequently, adhesiveness between the alloy film and the side surfaces of the groove may be reduced, to result in separation of the alloy film from the side surfaces of the groove. When the alloy film separates from the side surfaces of the groove, the barrier film made of MnSiO cannot be excellently formed on the separating portions.
If the alloy film is formed with a thickness not causing separation of the alloy film on the side surfaces of the groove, on the other hand, the thickness of a portion of the alloy film formed on the bottom surface of the groove is increased more than necessary. Consequently, the quantity of Mn contained in the alloy film is excessively increased, to disadvantageously cause an increase in wiring resistance resulting from the increased quantity of Mn remaining in the Cu wire.